Sometimes even that grand, looming sense of Ashes history has to take a back seat. For a session and a half this was instead a day to glory in the spectacle of individual achievement as Trent Bridge fell in love with a tall, gangly Australian teenager, with a wonderfully alluring sense of youthful ease in his cricketing movements and – yes – a lovely smile too. Ashton Agar, whose name is almost Ashes and almost a ton, almost scored an Ashes ton batting at No11 on his international debut, gliding, pulling, driving and generally romping his way to 98 before being dismissed playing the shot that would have brought up his hundred.

Australia has already swooned. Before retiring for the night the prime minister, Kevin Rudd, offered his tweeted approval for an Ashton Agar Day (which may or may not survive the morning briefings) and, propelled by approving messages from the likes of Hugh Jackman and Greg Norman, Agar-mania briefly loomed like a mushroom cloud above the babble of social media. Beyond this though, and beyond the dizzying array of batting records broken, the beauty of Agar's innings was simply its beauty, that sense of something uncluttered and cloudless on show, a wonderfully complete innings by an entirely natural 19-year-old cricketer.

"I'm super happy," Agar said, still in his baggy green, still looking like a kid trying on his uncle's hat, and quick to credit his coach with giving him the confidence to bat with such a ravishing sense of freedom. "Darren Lehmann just told the whole team to bat in their natural style and that's the way I like to bat, so that's what I did. I like to keep myself fairly relaxed and I didn't get too nervous. I was hitting the ball fairly well and I just tried to keep doing that."

Agar came out to bat an hour into the morning with England having taken five wickets for eight runs and Australia listing horribly on 117 for nine. He might have been dismissed on six, but was ruled not out by the TV umpire after a marginal call on a stumping off Graeme Swann. Despite this there was a compelling sense of looseness about his movements from the start: if there is anything better in life than being 19 years old and batting in an Ashes Test on a wonderfully sunlit Nottingham afternoon then clearly nobody has told Ashton Agar about it.

He is of course only masquerading as a No11, having appeared most recently at No7 for Western Australia, from where he made a match-winning 71 not out against Tasmania in February. But this is still a teenage debutant who six weeks ago was playing for Henley against North Mymms CC in the Home Counties Premier League and here had to start his innings against Swann and Jimmy Anderson. Unfazed by that stumping let-off he began to click through his own languid gears against Steven Finn, swivelling to play a lovely Gower-esque pull for four, before stepping inside and lofting Swann high over long-off for six with a true swing of the bat and a follow-through entirely devoid of tension.

And this, according to good judges in Australia, is the key to his game. From a young age Agar has been encouraged by his coaches to be loose, to move naturally, to allow his own obvious athleticism to drive his technique as a batsman and bowler. Having said that Finn, in particular, bowled poorly to the debutant at times, varying his lengths between short, shorter and horribly short as Agar surged through the foothills of his record-mangling ascent.

On 27 he passed the highest score by an Aussie No11 on debut. Trent Bridge purred and cooed and then applauded robustly as he reached 47, passing the highest score by any No11 on debut. At the other end Phil Hughes was briefly reduced to blocking out Swann so his 19-year old partner could score freely against the quicks. And still he kept on racking them up, becoming the first No11 to make 50 on debut with a languid run down to third man, and waggling his bat around winningly as Trent Bridge rose to cheer this entirely unexpected Australian teenager who had basically smiled his way through a wonderfully tense morning of Ashes cricket (it is, let us be clear once again, a lovely smile).

The players finally went to a delayed lunch with Agar on 69 not out, Australia on 229 for nine, and England retaining enough composure to offer a lovely impromptu guard of honour at the entrance to the pavilion. After lunch there was more of the same as Agar flicked Stuart Broad deftly through midwicket to go past his own highest score of 73 and into second place in the all-time No11s. A whip through midwicket drew murmurs of pleasure, while an attempted Finn yorker flayed through mid-on with flamingo-ish turn of the ankle was a source of minor wonder. It was, by now, all getting rather giddy as the Everest of that first hundred by a No11 began to loom on a dreamily sweltering afternoon. The previous highest 10th-wicket partnership, 154, came and went with Agar on 91. At 96 he eased past Tino Best's record for a No11 in Tests.

Now suddenly there was the first hint of tension as Broad produced some short stuff, hitting his upper arm and drawing a couple of errant swishes. Agar giggled and ran one down to third man to move to 98. Finally, though, mini-disaster: another short one was pulled, or rather elegantly miscued, to Swann, who took a tumbling catch before hurling the ball skywards with a sense of glee that, for a moment or two, almost seemed a little indecent.

The spell was broken though. Trent Bridge rose to applaud Agar, England's openers sprinted past and with a jiggling of the wires and a flicker of the picture this went back to being just a Test Match after all. Agar's innings will live on not only as a record score but as a moment of modern Ashes history. Before the end of play he even managed to draw a thick edge from Kevin Pietersen (put down by Brad Haddin) with his perky left-arm spin and Agar confirmed afterwards that he sees himself as a bowling, not batting all-rounder. Quite what the future holds for Australia's new star remains to be seen. But whatever it is we'll always have Trent Bridge.